Downhole oil and gas operations that involve gas injection include hydraulic fracturing, well servicing, and industrial maintenance.
Hydraulic fracturing is a common technique used to improve production from existing wells, low rate wells, new wells and wells that are no longer producing. Fracturing fluids and fracture propping materials are mixed in specialized equipment then pumped through a wellbore and into a subterranean formation containing the hydrocarbon materials to be produced. Injection of fracturing fluids that carry the propping materials is completed at high pressures sufficient to fracture the subterranean formation. The fracturing fluid carries the propping materials into the fractures. Upon completion of the fluid and proppant injection, the pressure is reduced and the proppant holds the fractures open. The well is then flowed to remove the fracturing fluid from the fractures and formation. Upon removal of sufficient fracturing fluid, production from the well is initiated.
Well servicing (also known as well intervention or well work) is an operation carried out on an oil or gas well during or at the end of its productive life, which alters the state of the well and/or well geometry, provides well diagnostics, or manages the production of the well.
It is also known to inject gases for oil and gas maintenance and testing operations within the scope of producing, refining and transporting hydrocarbons sourced from subterranean formations. Such maintenance and testing operations include pressuring, pressure testing, purging, displacement, carrying, inerting, catalyst regeneration, injectivity testing, capacity testing or drying within wells, facilities, refineries and pipelines.
Natural gas can be used as an injection gas in hydraulic fracturing operations. For example, Applicant's own PCT publication no. WO 2012/097426 discloses a method for hydraulically fracturing a formation in a reservoir using a fracturing fluid mixture comprising natural gas and a base fluid. The base fluid can comprise a conventional hydrocarbon well servicing fluid comprised of alkane and aromatic based hydrocarbon liquids with or without a gelling agent and proppant. This base fluid is combined with a gaseous phase natural gas stream to form the fracturing fluid mixture. In one embodiment, the natural gas can be provided from an LNG source, wherein the LNG is pressurized by a pump to a suitable fracturing pressure, and converted into vapor phase natural gas by a heater. More particularly, a heat source is disclosed which heats air that is driven across heat exchanger coils by a blower. The heat source can be generated without flame and may be waste heat or generated heat from an internal combustion engine, a catalytic burner or an electric element. Alternatively, the heat can be generated using a flame based heat source local to the heater or remote as dictated by safety requirements.
When a local flame is used to generate the heat, there is a risk of an unintended combustion event that may be harmful, if natural gas unexpectedly comes in contact with the local flame. Therefore, it is desirable to provide a means for heating LNG with a local flame that can address such a challenge.